This invention relates to machine controllers and, in particular, to controllers which utilize machine power consumption as a criterion for monitoring proper operation.
The need to automatically control machining operations has long been apparent to the industry. The demand for intricate designs to be formed in the workpiece and human limitations, as well as the limitations of the machinery have led to the ever increasing usage of automatic machine controllers to optimize the speed of the machining operation while at the same time preventing damage to the machine components. The earliest attempts in the art were relatively simple approaches in which a certain criterion was monitored and the machine shut off when a limit for the criterion was exceeded. However, as the years went by, the machine controllers became more and more complicated and expensive under the guise of being more sophisticated. In fact, in some of the most recent machine controllers at least nine different machine parameters are continuously monitored by exotic sensing devices and utilized to adaptively control machine cutting operations as a complex function of all the various criteria. (See e.g., U.S. Pat. No. 4,031,368 to Colding et al).
In addition to the increasing complexity of the art, known machine controllers have other perplexing problems. In general, the prior art systems immediately respond to an overlimit condition to alter the machine operation. Unfortunately, the overlimit conditions may not always be due to improper machine operation. This is especially true during machine start up, during diverse machining operations on workpieces which may have non-homogeneous structures, when the machine is being operated in an electrically noisy environment, etc. The prior art controllers generally will automatically shut off the machine in the event of these pseudo alarm conditions. This requires the operator to check the machine for damage, readjust the workpiece location, if necessary, and then restart the machining operation. In high volume production, this unnecessary down time becomes extremely expensive and results from the inability to discriminate between actual alarm conditions which would damage the machine and those conditions which similarly affect the monitored criteria but do not result in damage. The servosystems of the prior art controllers are also susceptible to non-stable operation. In the adaptive control mode, the feed rate change value is generated linearly by the system and may cause such a dramatic variation in the status quo that the machine will overshoot the desired level. Subsequently, the system will generate a change in the opposite direction to compensate for its overshot condition. This "ringing" can continue ad infinitum. Of course, these oscillations deleteriously affect the machining operation. Some attempts have been made to correct this problem by damping the linear response. However, machine response will be damped by the same factor at high error levels as at the more critical lower levels thereby preventing the machine operation to be quickly brought into conformity with the desired operating level when there is a large amount of error. Moreover, none of the prior art systems possess the capability of selectively adjusting the machine response characteristics in order to accomodate for different user applications and environments.
A common problem with known controllers is that they are particularly adapted to only one type of machine and do not possess the flexibility necessary for use in a wide variety of different machining applications. Accordingly, in a large plant, the user must be trained to operate many different types of controllers. This not only is time-consuming and inefficient but often it leads to tool damage from improper operation until the operator becomes familiar with the peculiarities of the controller. Therefore, there has been a substantial need for a universal machine controller which can be readily adapted to a wide variety of different applications and preferably one which is capable of controlling several different types of machining operations simultaneously.